Traditional Timber Roof With Purlins

Under purlins were typically propped off internal walls.

Traditional timber roof with purlins. 3 lean to roofs less common. A truss roof using factory made trusses which are delivered to site complete and just erected. Of course if there is intermediate support you can get away with a lighter and cheaper truss. Roof trusses can also span much greater distances without intermediate support than traditional beams purlins and joists.

The collar ties are used to connect the rafters preventing them from spreading outwards. The collar ties and hangers are used to improve the overall strength and stability of the roof. It is a horizontal bar that used to support building at the roof structurally. They give added support to the roof and also provide a nailing surface for the end panels and drip edge.

In lightweight timber roof construction under purlins were used to support rafters over longer spans than the rafters alone could span. Is possible compared with about 5m. There is an available purlin for every type of roofing material including purlin span for metal roof which is the most common material type to use this item. In traditional construction spans of over 3 metres or so were often dealt with by adding a purlin.

In traditional timber framing there are three basic types of purlin. It is a very common form of construction. Purlins are 2 by 4 feet and are installed much like metal roofing. This is a large timber running at right angles to the rafters and usually positioned mid span.

The roof support system is a ridgepole and either rafters which run perpendicular from the top of the walls to the ridge or purlins which run parallel to the ridge. Purlins are installed horizontally under metal roofs. A cut roof this is the traditional method of cutting the timber on site and building up the roof using rafters ridge boards joists and purlins etc the exact details being determined by the size of roof size of timbers etc. For example an 8 x 4 under purlin would support the center of a row of 6 x 2 rafters that in turn would support 3 x 2 roof purlins to which the roof cladding was fixed.

In architecture structural engineering or building a purlin is any longitudinal horizontal structural member in a roof except a type of framing with what is called a crown plate. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction. Video of traditional cut roof detail. A common arrangement is a rafter and purlin system which combines purlins and rafters.

All the figures are based on roofing tiles or slates laid on. Building control guidance note purlin and rafter. Purlin is a well known material in the field of architecture structural building or structural engineering. The purlins are supported by struts which in turn are supported on an internal load bearing wall.

There are two basic methods of pitched roof construction.